name of shellfish similar to clams?

I was in Japan recently this past July and had quite a few instances where I tried this shellfish (I think it is)… but I cannot remember the name for the life of me. I was not a fan, but I was told they were in season and they were much larger than a clam, but related. Can anyone help me with the name? I’ll know it if I see it. The sushi chef is preparing it in the video I’ve attached – hopefully that helps 🙂

name of shellfish similar to clams?
by u/beananamilk in sushi